Trenching study of the Mikata fault and reconstruction of crustal movements during the 1662 Kambun earthquake by historical records

Authors: Taku Komatsubara, Kiyohide Mizuno, Akira Sangawa and Haruo Yamazaki (Tokyo Metropolitan Univ.)

Abstract: The Mikata fault is an N-S-trending 15km-long active fault distirbuted in the western part of Fukui Prefecture to the north of Lake Biwa. We excavated three trenches on this fault. The trench survey has revealed that a reverse fault cuts debris flow deposits containing pottery fragments of the Heian Era (A.D. 794 to 1192). Therefore, it is concluded that the latest rupture on the Mikata fault occurred at least after the end of the 8th century. Many historical records show that distinct crustal movements occurred during the 1662 Kambun earthquake in the Mikata-goko
(five lakes) area on the west of the Mikata fault. We reviwed newly collected historical records and have clarified that at least 3 to 3.6 m uplift occurred in the area around 1 to 2 km west of the west-side-down Mikata fault during the earthquake. Such an uplift is ascribable to the activity of a submarine fault (Hiruga fault) and a flexure in Lake Suga,
which are arranged en echelon on the west of the Mikata fault. The result of trenching and review of historical records suggest that the Mikata fault moved together with the Hiruga fault and a flexure in Lake Suga during the 1662 earthquake.
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